Types of Anaerobic Reactors
There are five principal process variants which are proper in anaerobic wastewater treatment. These are as follows:
(1) Anaerobic Filter. The anaerobic filter is similar to a trickling filter in that a biofilm is generated on media. The bed is fully submerged and can be operated either upflow or downflow. For very high strength wastewaters, a recycle can be employed.
(2) Anaerobic Contact. This process can be considered as an anaerobic activated sludge because sludge is recycled from a clarifier or separator to the reactor. Since the material leaving the reactor is a gas-liquid-solid mixture, a vacuum degasifier is required to separate the gas and avoid floating sludge in the clarifier.
(3) Fluidized Bed. This reactor consists of a sand bed on which the biomass is grown. Since the sand particles are small, a very large biomass can be developed in a small volume of reactor. In order to fluidize the bed, a high recycle is required.
(4) Upflow Anaerobic Sludge Blanket (UASB). Under proper conditions anaerobic sludge will develop as high density granules. These will form a sludge blanket in the reactor. The wastewater is passed upward through the blanket. Because of its density, a high concentration of biomass can be developed in the blanket.
Anaerobic processes usually operate at a temperature of 35 C. In order to maintain this temperature, the methane gas generated in the process is used to heat the reactor. Anaerobic reactor types are show in the following figure.
Figure 11. Schematic diagrams of anaerobic wastewater treatment processes: (a) anaerobic filter reactor; (b) anaerobic contact reactor; (c) fluidized-bed reactor; (d) upflow anaerobic sludge blanket (UASB).